This paper presents the results of the G-AltiKa mission conducted along a SARAL-AltiKa track south-west of Ibiza (Balearic Islands, Western Mediterranean Sea) from 1 to 5 August 2013. The main feature of the mission is that the glider measurements are almost synchronous with the altimeter pass. The HF radar system operated by the Balearic Islands Coastal Observing and Forecasting System (SOCIB) constitutes a complementary tool to describe the circulation in the study area. The work is focused on the data processing step (interpolation, filtering, corrections) applied to the measurements and on the comparison of the geostrophic velocity across the satellite track. The absolute dynamic topography, computed by adding filtered 1 Hz and 40 Hz along-track sea-level anomalies Mediterranean Sea Mean Dynamic Topography, and the dynamic height, computed from glider temperature and salinity, both exhibited a signal characterized by weak gradients and amplitudes (2 cm), close to the expected accuracy of the AltiKa instrument. The corresponding geostrophic velocities and the HF radar velocities projected on the SARAL/AltiKa track all depicted a northwestward coastal current with a maximal velocity larger than 20 cm/s. The lack of synopticity due to the time interval between the satellite pass (August 1, 2013, 18:26:12 UTC) and the end of the glider transect (August 5, 2013, 04:17:22 UTC) resulted in a spatial shift between the glider and the altimeter along-track signal, around 5 km. The time evolution of the HF radar currents during the mission duration confirmed the plausibility of such a shift.
After the application of a 5 km lag to the glider dynamic height, the correlation and RMS difference between the different platforms were computed. The agreement between the altimetry, glider and HF radar cross-track velocities was synthesized in a Taylor diagram that evidenced the lowest root mean square difference (9.72 cm/s) and the highest correlation (0.64) between the velocities obtained from the glider dynamic height and those from the filtered 40 Hz sea-level anomalies. The 40 Hz data are particularly valuable as they enable us to use the SARAL-AltiKa data closer to the coast than typically possible with altimetry